手動修改Oracle sga方法有很多種，這裡只介紹其中一種，就是用oracle debug工具
    SQL> alter database open read only;

    Database altered.

    SQL> col scn for 9999999999999999
    SQL> select dbms_flashback.get_system_change_number scn from dual;

                  SCN
    —————–
       10999733447365

    SQL> oradebug setmypid
    Statement processed.
    SQL>  oradebug DUMPvar SGA kcsgscn_
    kcslf kcsgscn_ [060012658, 060012688) =  13346AC5 00000A01 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 60012338 00000000

    修改記憶體地址從0×060012658之後的4個位元組，內容為0xffffffff
    SQL> oradebug poke 0×060012658 4 0xffffffff
    BEFORE: [060012658, 06001265C) = 13346AC5
    AFTER:  [060012658, 06001265C) = FFFFFFFF

    SQL> oradebug DUMPvar SGA kcsgscn_
    kcslf kcsgscn_ [060012658, 060012688) =  FFFFFFFF 00000A01 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 60012338 00000000

    可以看到已經修改成功
    SQL> select dbms_flashback.get_system_change_number scn from dual;

                  SCN
    —————–
       11003706212351
      
    SQL> select current_scn scn from v$database;

                  SCN
    —————–
                    0